Arizona radiogenic helium dating laboratory
In our lab, selection of grains from mineral separates is done with one of two Leica MZ16 stereozoom microscopes.Samples can be examined, picked, and checked for inclusions under either cross-polarization with a rotating stage at 160x, or in plane-polarized darkfield illumination at 240x.
It can arguably be interpreted as an allegory for the history of thermochronology in general, in which early, presumably nonsensical or inconsistent ages are later interpreted as geologically meaningful cooling ages in the context of additional kinetic and geologic constraints (e.g., see review in Reiners et al., 2005).Watch Martin Pepper's awesome new videos of UA Geosciences' world-renowned field camp.Here is a sweet 12-minute version, and here is a beautiful 40-minute version to make you wish you did more fieldwork. Hoping to become even more confused about diagenesis?It's used for high-precision and -accuracy measurement of trace and major elements in a wide variety of natural materials.We make routine high precision measurements of U, Th, Sm, REE, Ca, and Zr for (U-Th)/He chronometry, and the instrument is also capable of analyzing a very broad range of trace and major elements in solutions and solids. There are essentially three steps to conventional (U-Th)/He dating: 1) selection, characterization, and preparation of grains for analysis, 2) He extraction and measurement, and 3) U-Th (and in some cases Sm) measurement.
Go here for a more detailed description of U-Th-Sm measurement.
Looking for amazing examples of voiceovers and cutaways?
See Marty Pepper's new blockbuster youtube video, Moki Marbles Matinee.
Because this distance is similar (within factor of ~10) as the size of typically dated crystals, an upward correction to the measured He (or downward correction to measured U, Th, and Sm) is required to account for He ejected from them (Farley et al., 1996; Hourigan et al., 2005).
This alpha-ejection correction ranges from about 20-40% of the measured age for zircon or apatite crystals with typical sizes.
Here we provide an overview of the procedures used in our lab, as of January 2007.